The U.S. National Highway Traffic Safety Administration said it opened a preliminary evaluation into the hybrid Camry sedans from model years 2007 and 2008 after receiving 59 complaints alleging intermittent loss of assisted braking, resulting in increased stopping distances.

A preliminary evaluation is the first step in a process that can lead to a recall should regulators determine that a manufacturer needs to address a safety problem.

Two accidents, but no injuries, were listed in the NHTSA documents. The complaints show an increasing trend, with more than half received in the past eight months, according to the NHTSA documents.

Each complaint alleges multiple incidents of either delayed braking activation or increased brake pedal effort, according to documents filed online with NHTSA. About 40 percent of the incidents occurred at speeds of 40 miles per hour or more, according to NHTSA.

A Toyota spokesman said the company was cooperating with the NHTSA's investigation.

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